1. Field of the Invention
The present invention relates to a magneto-resistive element and a magnetic memory, and more particularly, relates to a magneto-resistive element and a magnetic memory which enable writing by supplying spin-polarized electrons.
2. Description of the Related Art
Conventionally, there has been employed a method for applying a magnetic field in order to control a magnetization direction of a magnetic body. For example, in a hard disk drive, a magnetization direction of a medium is reversed by a magnetic field generated from a recording head, thereby carrying out writing. In addition, in a solid magnetic memory, a cell magnetization direction is controlled by applying to a cell a current magnetic field generated due to a current being supplied to a wire provided in the vicinity of a magneto-resistive effect element. The magnetization direct control by the external magnetic field has an old history, and can be said to be a reliable technique.
With recent advancement of nano-technology, on the other hand, remarkable downsizing of magnetic materials has becomes possible, and there has been a need for locally carrying out a magnetization control in a nano-scale. However, a magnetic field is essentially prone to spread in spatial, and thus, localization is difficult. In the case where a specific bit or cell is selected to control its magnetization direction as the bit or cell is downsized, a “cross-talk” problem that the adjacent bit or cell is affected by the magnetic field becomes serious. Further, if a magnetic field generation source is reduced in order to localize the magnetic field, there occurs a problem that a sufficiently generated magnetic field cannot be obtained.
Furthermore, in a recording element in which a magnetic body is provided as a medium, there is a danger that a recording state becomes unstable with respect to a disturbance referred to as a magnetic field. There has been a fatal problem that erasure of recording or incorrect information writing occurs due to a combination of the strength of an external magnetic field and a magneto-resistive element or a medial magnetic characteristic. A problem with a magnetic field having invaded as a disturbance may occur during writing. In this case, incorrect information is recorded.
In recent years, a “current direct drive type magnetization inversion” in which a current is supplied to a magnetic body, thereby causing magnetization inversion has been found out (refer to, for example, F. J. Albert, et al., Appl. Phy. Lett. 77, 3809 (2000)).
In this inversion, a current is spin-polarized by passing it through a magnetic layer, and the spin-polarized current is supplied, thereby inverting magnetization of a target magnetic layer. An angular motion quantity which the spin-polarized electron has is transmitted to and acts on an angular motion quantity of a magnetic body targeted to be magnetically inverted, thereby causing inversion of magnetization of that magnetic body. By using this phenomenon, it is possible to act on a nano-scaled magnetic body more intuitively, and also to carry out recording into a smaller magnetic body.
However, also in the case of utilizing the “current direct drive type magnetization inversion”, a change in recording state can occur due to a magnetic field having invaded as a disturbance. Further, in current driven writing, there is a problem that a current required for writing is changed due to the strength of an external magnetic field having invaded as a disturbance. Namely, there is a problem that incorrect information is recorded due to the magnetic field having invaded as a disturbance during writing. Furthermore, there is a problem associated with reliability because an element is destroyed due to a thermal effect caused by the current required for inversion.